Vaccine against Staphylococcus intoxication

ABSTRACT

Using nucleic acids encoding mutant SEA and SEB exotoxins from  Staphylococcus aureus , compositions and methods for use in inducing an immune response which is protective against  staphylococcal aureus  intoxication in subjects is described.

This application claims the benefit of provisional application No.60/092,416 filed Jul. 10, 1998.

FIELD OF THE INVENTION

This invention relates to vaccines for bacterial toxins fromStaphylococcus aureus.

INTRODUCTION

The most common cases of food poisoning are caused by the bacteriaStaphylococcus aureus. Exotoxins produced by the organism causegastrointestinal distress, to include diarrhea and vomiting, and canalso cause toxic shock syndrome which may lead to death. These exotoxinsalso called enterotoxins since they typically exert their effects on thegastrointestinal tract, cause disease by binding to the majorhistocompatibility complex (MHC) on T-cells which results in the releaseof large amounts of various cytokines. This cytokine release has beenpostulated to mediate the many toxic effects of the S. aureus exotoxins.There are at least eight antigenically distinct exotoxins (labeled SEA,SEB, SEC1, SEC2, SEC3, SED, SEE, and SEG) produced by S. aureus.Presently, there is no approved/licensed SEA or SEB vaccine. Treatmentfor Staphylococcus aureus infections is becoming more difficult sincethe organism has become resistant to most antibiotics.

Therefore, there is a need for an efficacious vaccine protective againstStaphylococcus aureus intoxication.

SUMMARY OF THE INVENTION

The present invention satisfies the need discussed above. The presentinvention relates to a method and composition for use in inducing animmune response which is protective against intoxication withStaphylococcus aureus.

In this application is described a vaccine strategy where a gene codingfor a protein of interest is cloned in a VEE virus vector in place ofthe VEE virus structural genes; the result is a self-replicating RNAmolecule, a replicon, that encodes its own replicase and transcriptasefunctions, and in addition makes abundant quantities of mRNA encodingthe foreign protein. When replicon RNA is transfected into eukaryoticcells along with two helper RNAs that express the VEE structuralproteins (glycoproteins and nucleocapsid), the replicon RNA is packagedinto VEE virus-like particles by the VEE virus structural proteins,which are provided in trans. Since the helper RNAs lack packagingsignals neccessary for further propagation, the resulting VEE repliconparticles (VRPs) which are produced are infectious for one cycle but aredefective thereafter. Upon infection of an individual cell with a VRP,an abortive infection occurs in which the infected cell produces theprotein of interest in abundance, is ultimately killed by the infection,but does not produce any viral progeny (Pushko et al., 1997, Virology239, 389-401).

Genes encoding a mutant SEA (mSEA) exotoxin and a mutant SEB (mSEB)exotoxin were each inserted into the VEE replicon vaccine vector (FIG.1). The mutant gene product is unable to bind to the MHC on T-cells(Bavari, et al., 1996, Vaccines 96, 135-141). Evaluation of themSEA-replicon and mSEB-replicon in vitro have shown high levelexpression of both bacterial proteins. Balb/c mice immunized with themSEB-replicon produced high specific antibody titers and were protectedwhen challenged intraperitoneally with wild type SEB.

Therefore, it is one object of the present invention to provide a VEEvirus replicon vector comprising a VEE virus replicon and a DNA fragmentencoding a mutant SEA exotoxin or a mutant SEB exotoxin.

It is another object of the present invention to provide a selfreplicating RNA comprising the VEE virus replicon and any of the SEA orSEB fragments described above.

It is another object of the present invention to provide infectious VEEvirus replicon particles produced from the VEE virus replicon RNAdescribed above.

It is further an object of the invention to provide an immunologicalcomposition for the protection of mammals against Staphylococcus aureusintoxication comprising VEE virus replicon particles containing any ofthe Staphylococcus aureus fragments described above or a combination ofdifferent VEE virus replicons each having a different Staphylococcusaureus fragment.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims, and accompanying drawings where:

FIG. 1. Diagram of the mSEA and mSEB replicon constructs. The repliconsare similar to the full-length VEE RNA except that the open readingframe encoding the VEE structural proteins was replaced with either themSEA or mSEB genes.

FIG. 2. Western blot of BHK cell lysates showing expression of mSEA ormSEB (containing a 5′ prokaryotic secretory signal) from recombinant VEEreplicons. a) transfected cell lysate; b) infected cell lysate; c)commercially available product.

FIG. 3. Schematic diagram of replicon constructs containing mutant SEAor mutant SEB DNA fragments.

DETAILED DESCRIPTION

In the description that follows, a number of terms used in recombinantDNA, virology and immunology are extensively utilized. In order toprovide a clearer and consistent understanding of the specification andclaims, including the scope to be given such terms, the followingdefinitions are provided.

Replicon

A replicon is equivalent to a full length virus from which all of theviral structural proteins have been deleted. A multiple cloning site canbe cloned into the site previously occupied by the structural proteingenes. Virtually any heterologous gene may be cloned into this cloningsite.

Transcription of the RNA from the replicon yields an RNA capable ofinitiating infection of the cell identically to that seen with thefull-length infectious virus clone. However, in lieu of the viralstructural proteins, the heterologous antigen is expressed. This systemdoes not yield any progeny, virus particles because there are no viralstructural proteins available to package the RNA into particles.

Particles which appear structurally identical to virus particles can beproduced by supplying structural proteins for packaging of the repliconRNA in trans. This is typically done with two helpers also calleddefective helper RNAs. One helper consists of a full length infectiousclone from which the nonstructural protein genes and the glycoproteingenes are deleted. The helper retains only the terminal nucleotidesequences, the promoter for subgenomic mRNA transcription and thesequences for the viral nucleocapsid protein. The second helper isidentical to the first except that the nucleocapsid gene is deleted andonly the glycoprotein genes are retained. The helper RNA's aretranscribed in vitro and co-transfected with replicon RNA. Because thereplicon RNA retains the sequences for packaging by the nucleocapsidprotein, and because the helpers lack these sequences, only the repliconRNA is packaged by the viral structural proteins and released from thecell. The particles can then be inoculated into animals similar toparent virus. The replicon particles will initiate only a single roundof replication because the helpers are absent, they produce no progenyvirus particles, and express only the viral nonstructural proteins andthe product of the heterologous gene cloned in place to the structuralproteins.

The VEE virus replicon is a genetically reorganized version of the VEEvirus genome in which the structural proteins genes are replaced with agene from an immunogen of interest, in this invention, thestaphylococcal proteins. The result is a self replicating RNA (replicon)that can be packaged into infectious particles using defective helperRNAs that encode the glycoprotein and capsid proteins of the VEE virus.

Subject

Includes both human, animal, e.g., horse, cattle, donkey, monkey, pig,dog, guinea pig, mouse, hamster, avian e.g., chicken; pheasant orturkey, fish and other marine animals, and insects such as mosquito.

In one embodiment, the present invention relates to a recombinant DNAmolecule that includes a VEE replicon and a DNA sequence encoding mutantStaphylococcus aureus A and B exotoxins. The sequence mSEA and mSEB hasbeen determined and is presented in SEQ ID NO:1 and SEQ ID NO:2,respectively. In addition, isolated nucleic acid molecules of theinvention include DNA molecules which comprise a sequence substantiallydifferent from those described above but which, due to the degeneracy ofthe genetic code, still encode the Staphylococcus aureus proteinsdescribed. Of course, the genetic code and species-specific codonpreferences are well known in the art. Thus, it would be routine for oneskilled in the art to generate the degenerate variants described above,for instance, to optimize codon expression for a particular host (e.g.,change codons in the human mRNA to those preferred by a bacterial hostsuch as E.coli).

Nucleic acid molecules of the present invention may be in the form ofRNA, or in the form of DNA, including, for instance, cDNA and genomicDNA obtained by cloning or produced synthetically. The DNA may bedouble-stranded or single-stranded. Single-stranded DNA or RNA may bethe coding strand, also known as the sense strand, or it may be thenon-coding strand, also referred to as the antisense strand.

By “isolated” nucleic acid molecule(s) is intended a nucleic acidmolecule, DNA or RNA, which has been removed from its nativeenvironment. For example, recombinant DNA molecules contained in avector are considered isolated for the purposes of the presentinvention. Further examples of isolated DNA molecules includerecombinant DNA molecules maintained in heterologous host cells orpurified (partially or substantially) DNA molecules in solution.Isolated RNA molecules include in vivo or in vitro RNA transcripts ofthe DNA molecules of the present invention. Isolated nucleic acidmolecules according to the present invention further include suchmolecules produced synthetically.

The present invention is further directed to nucleic acid moleculescomprising portions or fragments of the nucleotide sequences describedherein. Fragments include portions of the nucleotide sequences of atleast 10 contiguous nucleotides in length selected from any twointegers, one of which representing a 5′ nucleotide position and asecond of which representing a 3′ nucleotide position, where the firstnucleotide for each nucleotide sequence is position 1. That is, everycombination of a 5′ and 3′ nucleotide position that a fragment at least10 contiguous nucleotide bases in length or any integer between 10 andthe length of an entire nucleotide sequence minus 1.

The present invention further relates to variants of the nucleic acidmolecules of the present invention, which encode portions, analogs orderivatives of the Staphylococcus aureus polypeptides described above.Variants may occur naturally, such as a natural allelic variant. By an“allelic variant” is intended one of several alternate forms of a geneoccupying a given locus of a chromosome of an organism. Non-naturallyoccuring variants may be produced by known mutagenesis techniques. Suchvariants include those produced by nucleotide substitution, deletion oraddition of one or more nucleotides in the coding or noncoding regionsor both. Alterations in the coding regions may produce conservative ornonconservative amino acid substitutions, deletions, or additions.Especially preferred among these are silent substitutions, additions,and deletions which do not alter the properties and activities of theStaphylococcus aureus polypeptides disclosed herein or portions thereof.Also preferred in this regard are-conservative substitutions.

In another embodiment, the present invention relates to a recombinantDNA molecule that includes a vector and a DNA sequence as describedabove. The vector can take the form of a plasmid, phage, cosmid, YAC,eukaryotic expression vector such as a DNA vector, Pichia pastoris, or avirus vector such as for example, baculovirus vectors, retroviralvectors or adenoviral vectors, and others known in the art. The clonedgene may optionally be placed under the control of (i.e., operablylinked to) certain control sequences such as promoter sequences, orsequences which may be inducible and/or cell type-specific. Suitablepromoters will be known to a person with ordinary skill in the art. Theexpression construct will further contain sites for transcriptioninitiation, termination and, in the transcribed region, a ribosomebinding site for translation. When the DNA sequences described above arein a replicon expression system, such as the VEE replicon describedabove, the proteins can be expressed in vivo. The DNA sequence for anyof the Staphylococcus aureus proteins described above can be cloned intothe multiple cloning site of a replicon such that transcription of theRNA from the replicon yields an infectious RNA containing theStaphylococcus aureus protein or proteins of interest. Use of helper RNAcontaining sequences necessary for encapsulation of the viral transcriptwill result in the production of viral particles containing replicon RNAwhich are able to infect a host and initiate a single round ofreplication resulting in the expression of the Staphylococcus aureusproteins. Such replicon constructs include those specified in Table 1.

TABLE 1 Replicon Plasmid Name Serotype expresses p3014-56SEA SEA mutatedSEA p3014-55SEB SEB mutated SEB p3014-57SEB SEB prokaryotic secretorysequence-mutated SEB

These three plasmids were deposited with the American Type CultureCollection, located at 10801 University Blvd., Manassas, Va. 20110-2209,USA, on Feb. 1, 2002, under the conditions of the Budapest Treaty.Plasmid p3014-56SEA was assigned the deposit designation PTA-4033;plasmid p3014-55SEB was assigned the deposit designation PTA-4032; andplasmid p3014-57SEB was assigned the deposit designation PTA4034.

In another embodiment, the present invention relates to RNA moleculesresulting from the transcription of the constructs described above. TheRNA molecules can be prepared by in vitro transcription using methodsknown in the art and described in the Examples below. Alternatively, theRNA molecules can be produced by transcription of the constructs invivo, and isolating the RNA. These and other methods for obtaining RNAtranscripts of the constructs are known in the art. Please see CurrentProtocols in Molecular Biology. Frederick M. Ausubel et al. (eds.), JohnWiley and Sons, Inc. The RNA molecules can be used, for example, as anucleic acid vaccine, or to transfect cells along with RNA from helperplasmids, one of which expresses VEE glycoproteins and the other VEEcapsid proteins, as described above, in order to obtain repliconparticles.

Introduction of the construct into the host cell can be effected bycalcium phosphate transfection, electroporation, infection, and othermethods known in the art and described in standard laboratory manualssuch as Current Protocols in Molecular Biology, Ausubel, F. M. et al.(Eds), Wiley & Sons, Inc. All documents cited herein supra and infra arehereby incorporated in their entirety by referece thereto.

In a further embodiment, the present invention relates to host cellsstably transformed or transfected with the above-described recombinantDNA constructs. The host cell can be prokaryotic (for example,bacterial), lower eukaryotic (for example, yeast or insect) or highereukaryotic (for example, all mammals, including but not limited to ratand human). Both prokaryotic and eukaryotic host cells may be used forexpression of desired coding sequences when appropriate controlsequences which are compatible with the designated host are used. Amongprokaryotic hosts, E. coli is most frequently used. Expression controlsequences for prokaryotes include promoters, optionally containingoperator portions, and ribosome binding sites. Transfer vectorscompatible with prokaryotic hosts are commonly derived from, forexample, pBR322, a plasmid containing operons conferring ampicillin andtetracycline resistance, and the various pUC vectors, which also containsequences conferring antibiotic resistance markers. These markers may beused to obtain successful transformants by selection. Please see e.g.,Maniatis, Fitsch and Sambrook, Molecular Cloning: A Laboratory Manual(1982) or DNA Cloning, Volumes I and II (D. N. Glover ed. 1985) forgeneral cloning methods. The DNA sequence can be present in the vectoroperably linked to a sequence encoding an IgG molecule, an adjuvant, acarrier, or an agent for aid in purification of protein of theinvention, such as glutathione S-transferase. The recombinant moleculecan be suitable for transfecting eukaryotic cells, for example,mammalian cells and yeast cells in culture systems. Saccharomycescerevisiae, Saccharomyces carlsbergensis, and Pichia pastoris are themost commonly used yeast hosts, and are convenient fungal hosts. Controlsequences for yeast vectors are known in the art. Mammalian cell linesavailable as hosts for expression are known in the art and include manyimmortalized cell lines available from the American Type CultureCollection (ATCC), such as baby hamster kidney (BHK) cells, MRC-5 cells,and vero cells, to name a few. Suitable promoters are also known in theart and include viral promoters such as that from SV40, Rous sarcomavirus (RSV), adenovirus (ADV), bovine papilloma virus (BPV), andcytomegalovirus (CMV). Mammalian cells may also require terminatorsequences and poly A addition sequences; enhancer sequences whichincrease expression may also be included, and sequences which causeamplification of the gene may also be desirable. These sequences areknown in the art. The transformed or transfected host cells can be usedas a source of DNA sequences described above. When the recombinantmolecule takes the form of an expression system, the transformed ortransfected cells can be used as a source of the protein describedbelow.

A polypeptide or amino acid sequence derived from the amino acidsequences mentioned above, refers to a polypeptide having an amino acidsequence identical to that of a polypeptide encoded in the sequence, ora portion thereof wherein the portion consists of at least 2-5 aminoacids, and more preferably at least 8-10 amino acids, and even morepreferably at least 11-15 amino acids, or which is immunologicallyidentifiable with a polypeptide encoded in the sequence.

A recombinant or derived polypeptide is not necessarily translated froma designated nucleic acid sequence; it may be generated in any manner,including for example, chemical synthesis, or expression of arecombinant expression system. In addition the polypeptide can be fusedto other proteins or polypeptides which increase its antigenicity, suchas adjuvants for example.

The recombinant or fusion protein can be used as a vaccine for immunityagainst staphycococcal intoxication or as a diagnostic tool fordetection of staphylococcus exotoxin. The transformed host cells can beused to analyze the effectiveness of drugs and agents which inhibitStaphylococcus aureus exotoxins or release of the exotoxins, such ashost proteins or chemically derived agents or other proteins which mayinteract with Staphylococcus aureus proteins of the present invention toinhibit its function. A method for testing the effectiveness of ananti-staphylococcus drug or agent can be, for example, mixing theantisera, drug, or agent with the enterotoxins and then injecting themixture into a naïve mouse. If the mouse survives, then the drug oragent is effective at preventing intoxication. In other words, passivetransfer of sera/antibodies is used to evaluate whether or not an agentcan be neutralized by antibodies only (a humoral immune response), or ifa cytotoxic T cell respone is necessary (a cellular immune response).

In another embodiment, the present invention relates to a vaccineagainst staphylococcal intoxication comprising one or more repliconparticles derived from one or more replicons encoding one or moreStaphylococcus aureus proteins or polypeptides as described above. Thepresent invention relates to a method for providing immunity againststaphylococcal intoxication said method comprising administering one ormore replicon particles containing any combination of the Staphylococcusaureus proteins to a subject such that a protective immune reaction isgenerated. In addition, the replicon can optionally contain a second ormore antigens for which protection is desired since the replicon vectorcan accomodate up to 5 kb of foreign sequence. The additional antigenscan induce additional and different desired immunity, or can be used forincreasing the immunogenicity of the first antigen. Other uses and otherantigens will be evident to a person with ordinary skill in the art uponreading the present application. Serological cross-protection has beenfound between A and E, and B and C exotoxins (Spero and Metzger, 1981,Methods in Enzymology 78, 331-336). It is therefore possible thatimmunization with one serotype will provide protection from intoxicationwith another serotype.

Vaccine formulations of the present invention comprise an immunogenicamount of a replicon particle, resulting from one of the repliconconstructs described above, or a combination of replicon particles as amultivalent vaccine, in combination with a pharmaceutically acceptablecarrier. An “immunogenic amount” is an amount of the replicon particlessufficient to evoke an immune response in the subject to which thevaccine is administered. An amount of from about 10² to 10⁷ per dose issuitable, more or less can be used depending upon the age and species ofthe subject being treated. Exemplary pharmaceutically acceptablecarriers include, but are not limited to, sterile pyrogen-free water andsterile pyrogen-free physiological saline solution.

Administration of the replicon particles disclosed herein may be carriedout by any suitable means, including both parenteral injection (such asintraperitoneal, subcutaneous, or intramuscular injection), by in ovoinjection in birds, orally and by topical application of the virus(typically carried in the pharmaceutical formulation) to an airwaysurface. Topical application of the virus to an airway surface can becarried out by intranasal administration (e.g. by use of dropper, swab,or inhaler which deposits a pharmaceutical formulation intranasally).Topical application of the virus to an airway surface can also becarried out by inhalation administration, such as by creating respirableparticles of a pharmaceutical formulation (including both solidparticles and liquid particles) containing the replicon as an aerosolsuspension, and then causing the subject to inhale the respirableparticles. Methods and apparatus for administering respirable particlesof pharmaceutical formulations are well known, and any conventionaltechnique can be employed. An “immunogenic amount” is an amount of thereplicon particles sufficient to evoke an immune response in the subjectto which the vaccine is administered.

When the replicon RNA or DNA is used as a vaccine, the replicon RNA orDNA can be administered directly using techniques such as delivery ongold beads (gene gun), delivery by liposomes, or direct injection, amongother methods known to people in the art. Any one or more constructs orreplicating RNA described above can be use in any combination effectiveto elicit an immunogenic response in a subject. Generally, the nucleicacid vaccine administered may be in an amount of about 1-5 ug of nucleicacid per dose and will depend on the subject to be treated, capacity ofthe subject's immune system to develop the desired immune response, andthe degree of protection desired. Precise amounts of the vaccine to beadministered may depend on the judgement of the practitioner and may bepeculiar to each subject and antigen.

The vaccine may be given in a single dose schedule, or preferably amultiple dose schedule in which a primary course of vaccination may bewith 1-10 separate doses, followed by other doses given at subsequenttime intervals required to maintain and or reinforce the immuneresponse, for example, at 1-4 months for a second dose, and if needed, asubsequent dose(s) after several months. Examples of suitableimmunization schedules include: (i) 0, 1 months and 6 months, (ii) 0, 7days and 1 month, (iii) 0 and 1 month, (iv) 0 and 6 months, or otherschedules sufficient to elicit the desired immune responses expected toconfer protective immunity, or reduce disease symptoms, or reduceseverity of disease.

The following MATERIALS AND METHODS were used in the examples thatfollow.

The Venezuelan equine encephalitis (VEE) virus replicon vaccine vectorsystem was used for the mutagenized, non-toxic staphylococcalenterotoxin A (mSEA) or B (mSEB) protein. This system is composed of aself-replicating RNA expression vector (replicon) containing all of theVEE virus non-structural genes and a heterologous gene (e.g. mSEA, ormSEB) in place of the VEE structural genes. Cotransfection (byelectroporation) of cells in vitro with a replicon and two helper RNAmolecules, the latter encoding all of the VEE structural proteins,results in the production of propagation-deficient VEE repliconparticles (VRPs). The mSEA and mSEB-replicons were efficiently packagedinto VRPs using the double helper system. Stock solution's containedabout 10⁸ iu of purified VRP per milliliter.

Replicon p3014-56SEA was cloned as follows: The plasmid pETA489270Ccontaining the mutant SEA gene (SEQ ID NO:1) was linearized using Nde Iand the overhanging ends were filled in using DNA polymerase I. Next theplasmid was cut with Hind III which released the SEA gene. The gene wasligated into the KS2 shutle, which was previously linearized with EcoRI, filled in using DNA polymerase I, and then cut with Hind III. Thegene was cut out of the shuttle using Apa I and Not I and then ligatedinto the replicon pVR2 (Drawing sheet 1, U.S. Pat. No. 5,792,462Johnston et al.).

Replicon p3014-55SEB was cloned as follows: The plasmid pETASEB3containing a mutant SEB gene without a secretory signal (SEQ ID NO:3)was linearized using Nde I and then the overhanging ends were filled inusing DNA polymerase I. Next the plasmid was cut with EcoR I whichreleased the SEB gene. The gene was ligated into the KS1 shutle, whichwas previously linearized with BamH I, filled in using DNA polymerase I,and then cut with EcoR I. The gene was cut out of the shuttle using ApaI and Not I and then ligated into the replicon pVR2.

Replicon p3014-57SEB was cloned as follows: The plasmid pETB899445Pcontaining a mutant SEB gene (SEQ ID NO:2) was linearized using Nde Iand then the overhanging ends were filled in using DNA polymerase I.Next, the plasmid was cut with BamH I which released the SEB genecontaining a prokaryotic secretory signal. The gene was ligated into theKS2 shutle, which was previously linearized-with EcoR I, filled in usingDNA polymerase I, and then cut with BamH I. The gene was cut out of theshuttle using Apa I and Not I and then ligated into the replicon pVR2.

VRPs containing replicons encoding the above bacterial genes werepurified from BHK cell culture supernatants by ultracentrifugationthrough a discontinuous sucrose gradient (20%) to remove cell cultureimpurities. After reconstituting the pelleted VRP in phosphate bufferedsaline, the VRPs were stored at −70 degrees centigrade and showed noloss in concentration or activity. Cells infected with repliconsencoding mutagenized SEA or SEB expressed high levels of these proteinswhen analyzed by western blot (FIG. 2). VRPs were tittered using animmunofluorescence assay in cultures of BHK cells and expressed as focusforming units (FFU). One FFU is equivalent to one infectious unit. VRPpreparations were monitored for the generation of replication competentVEE virus using a standard plaque forming assay. No plaque forming units(PFU) were found in any of the replicon preparations.

For the enzyme-linked immunosorbent assay (ELISA), microtiter plateswere coated with antigen (0.5 ug/ml) in PBS and allowed to absorbovernight at 4° C. Four fold serum dilutions in blocking buffer wereapplied to the plates and incubated at 37° C. for 1 hour. After washing,an anti-mouse secondary antibody (HRP conjugated) was added to the plateand incubated for an additional hour at 37° C. After washing, boundantibody was detected colormetrically using ABTS as a substrate.

BALB/c mice were inoculated subcutaneously with 10⁵ to 10⁷ FFU of VRPcontaining the mSEB-replicon two or three times at 28 day intervals.Control mice were inoculated with 10 ug of mSEB absorbed to 0.28%alhydrogel (EM Sergeant Pulp and Chemical Co. Inc., Clifton, N.J.) or10⁷ infectious units of the Lassa N replicon subcutaneously two or threetimes at 28 day intervals. The mice were intraperitoneally challenged 28days after the last inoculation with wild type SEB (1.25 ug orapproximately 5 LD₅₀) and then four hours later with LPS (40 ug).

EXAMPLE 1 Staphylococcal Enterotoxin A and B Studies

Cells infected with replicons encoding either mutagenized SEA or SEBexpressed high levels of these proteins as demonstrated by western blot.VEE replicons expressing the mutated SEA or SEB genes produced proteinsthat comigrated on gels with authentic toxin protein and reactedefficiently with antibodies raised to the authentic proteins (FIG. 2).The mSEA and mSEB-replicons were efficiently packaged into VRPs usingthe double helper system. Stock solutions contained about 10⁸ iu ofpurified VRP per milliliter. No replication competent virus was detectedin any of the preparations. The VRPs containing the SEA-replicon andSEB-replicon were characterized using an immunofluorescence assay andshown to produce immunoreactive proteins in eukaryotic cell cultures.The results of the animal studies showed that the SEB-replicon couldimmunize and protect mice from a lethal challenge of wild type SEB.Table 2 shows survival and ELISA results for mice inoculated 2 or 3times with 10⁵, 10 ⁶, or 10⁷ FFU of VRP containing the mSEB-replicon.The mSEB-replicon protected the mice as well as the previously reportedmutagenized mSEB/alum vaccine (Bavari, 1996, supra). The mSEB-repliconstimulated a dose dependent antibody response in BALB/c mice withprotection correlating directly with serum ELISA titers to SEB.

TABLE 2 SEB replicon protects Balb/c mice from wild type SEB ChallengeNo. of Survived inoculum dose¹ inoculations² total GMT SEB/alum 10 μg 210/10 1882027 SEB/alum 10 μg 3 15/19 n.d. Lassa N Rep 10⁷ 2  0/10 93Lassa N Rep 10⁷ 3 0/5 n.d. SEB Rep 10⁵ 2  0/10 186 SEB Rep 10⁵ 3  1/20n.d. SEB Rep 10⁶ 2  1/10 2785 SEB Rep 10⁶ 3  4/20 n.d. SEB Rep 10⁷ 2 3/10 4222 SEB Rep 10⁷ 3 15/20 n.d. Challenge Challenge controlsmaterial Lassa N Rep 10⁷ 2 5/5 SEB only Lassa N Rep 10⁷ 3 5/5 SEB onlyLassa N Rep 10⁷ 2 5/5 LPS only Lassa N Rep 10⁷ 3 5/5 LPS only ¹Eithermicrograms of protein or infectious units of replicon per dose;²inoculations were given 28 days apart; n.d., not determined; GMT,geometric mean titer.

C57BL/6 mice were given 2 or 5 inoculations of mSEA-VRP, 28 days apart,and them challenged 28 days after the last inoculation. The repliconimmunized mice failed to produce antibodies and were not protected froman SEA challenge. Swiss mice were given 3 inoculations of mSEA-VRP 28days apart or 4 inoculations 21 days apart failed to produce antibodies.Right now, we do not understand why the mice are not responding, butplan on conducting another study looking at a prime and boost schemeusing a combination of replicon and mSEA/alhydrogel.

3 1 757 DNA Staphyloccus aureus 1 atgagaaaag cgaagaaata aatgaaaaagatttgcgaaa 40 aaagtctgaa ttgcagggaa cagctttagg caatcttaaa 80 caaatctattattacaatga aaaagctaaa actgaaaata 120 aagagagtca cgatcaattt cgacagcatactatattgtt 160 taaaggcttt tttacagatc attcgtggta taacgattta 200ttagtacgtt ttgattcaaa ggatattgtt gataaatata 240 aagggaaaaa agtagacttgtatggtgctt atgctggtta 280 tcaatgtgcg ggtggtacac caaacaaaac agcttgtatg320 tatggtggtg taacgttaca tgataataat cgattgaccg 360 aagagaaaaaagtgccgatc aatttatggc tagacggtaa 400 acaaaataca gtacctttgg aaacggttaaaacgaataag 440 aaaaatgtaa ctgttcagga gttggatctt caagcaagac 480gttatttaca ggaaaaatat aatttatata actctgatgt 520 ttttgatggg aaggttcagaggggattaat cgtgtttcat 560 acttctacag aaccttcggt taattacgat ttatttggtg600 ctcaaggaca gtattcaaat acactattaa gaatatatag 640 agataataaaacgattaact ctgaaaacat gcatattgat 680 atatatttat atacaagtta aacatggtagttttgaccaa 720 cgtaatgttc agattattat gaaccgagaa taatcta 757 2 801 DNAStaphylococcus aureus 2 atgtataaga gattatttat ttcacatgta attttgatat 40tcgcactgat attagttatt tctacaccca acgttttagc 80 agagagtcaa ccagatcctaaaccagatga gttgcacaaa 120 tcgagtaaat tcactggttt gatggaaaat atgaaagttt160 tgtatgatga taatcatgta tcagcaataa acgttaaatc 200 tatagatcaatttcgatact ttgacttaat atattctatt 240 aaggacacta agttagggaa ttatgataatgttcgagtcg 280 aatttaaaaa caaagattta gctgataaat acaaagataa 320atacgtagat gtgtttggag ctaatgctta ttatcaatgt 360 gctttttcta aaaaaacgaatgatattaat tcgcatcaaa 400 ctgacaaacg aaaaacttgt atgtatggtg gtgtaactga440 gcataatgga aaccaattag ataaatatag aagtattact 480 gttcgggtatttgaagatgg taaaaattta ttatcttttg 520 acgtacaaac taataagaaa aaggtgactgctcaagaatt 560 agattaccta actcgtcact atttggtgaa aaataaaaaa 600ctctatgaat ttaacaactc gccttatgaa acgggatata 640 ttaaatttat agaaaatgagaatagctttt ggtatgacat 680 gatgcctgca ccaggagata aatttgacca atctaaatat720 ttaatgatgt acaatgacaa taaaatggtt gattctaaag 760 atgtgaagattgaagtttat cttacgacaa agaaaaagtg 800 a 801 3 723 DNA Staphylococcusaureus 3 atggagagtc aaccagatcc taaaccagat gagttgcaca 40 aatcgagtaaattcactggt ttgatggaaa atatgaaagt 80 tttgtatgat gataatcatg tatcagcaataaacgttaaa 120 tctatagatc aatttcgata ctttgactta atatattcta 160ttaaggacac taagttaggg aattatgata atgttcgagt 200 cgaatttaaa aacaaagatttagctgataa atacaaagat 240 aaatacgtag atgtgtttgg agctaatgct tattatcaat280 gtgctttttc taaaaaaacg aatgatatta attcgcatca 320 aactgacaaacgaaaaactt gtatgtatgg tggtgtaact 360 gagcataatg gaaaccaatt agataaatatagaagtatta 400 ctgttcgggt atttgaagat ggtaaaaatt tattatcttt 440tgacgtacaa actaataaga aaaaggtgac tgctcaagaa 480 ttagattacc taactcgtcactatttggtg aaaaataaaa 520 aactctatga atttaacaac tcgccttatg aaacgggata560 tattaaattt atagaaaatg agaatagctt ttggtatgac 600 atgatgcctgcaccaggaga taaatttgac caatctaaat 640 atttaatgat gtacaatgac aataaaatggttgattctaa 680 agatgtgaag attgaagttt atcttacgac aaagaaaaag 720 tga 723

What is claimed is:
 1. A recombinant DNA construct comprising: (i) a VEEvirus replicon vector which contains (ii) an isolated nucleic acidfragment comprising the nucleic acid sequence encoding mSEA, whichsequence expresses a peptide product that does not bind to MHC onT-cells.
 2. A recombinant DNA construct according to claim 1 whereinsaid vector is an expression vector.
 3. A recombinant DNA constructaccording to claim 1, wherein said vector further comprises aprokaryotic vector.
 4. An isolated host cell transformed with arecombinant DNA construct according to claim
 1. 5. A host cell accordingto claim 4 wherein said host cell is prokaryotic.
 6. A host cellaccording to claim 4 wherein said host cell is eukaryotic.
 7. A methodfor producing Staphylococcus aureus protein comprising culturing thecells according to claim 5 under conditions such that said DNA fragmentis expressed and said protein is produced.
 8. A method for producingStaphylococcus aureus protein comprising culturing the cells accordingto claim 6 under conditions such that said DNA fragment is expressed andsaid protein is produced.
 9. A recombinant DNA construct comprising: (i)a VEE virus replicon vector which contains (ii) an isolated nucleic acidfragment comprising the nucleic acid sequence encoding mSEA SEQ ID NO:1.